The deployment of digital-subscriber-line (DSL) services typically involves deployment of DSL based units in the digital line carrier (DLC) environment. Such deployment creates a need to cost effectively back haul T1 circuits from DLC street cabinets to asynchronous transfer mode (ATM) networks.
Typically the back hauling of T1 circuits and termination into an ATM network is achieved by one of the following: (1) terminating directly on an ATM edge switch, (2) terminating on a DSL Access Multiplexer (DSLAM), and (3) terminating on a multi-service access platform.
Implementation of termination directly on the ATM switch typically requires termination of groups of inverse-multiplexers ATM (IMA) directly on the ATM switch. In such a case, the bandwidth available per slot of the ATM switch is typically much higher than the available space to locate IMA functionality and thus common equipment features of the ATM switch are not used cost effectively.
When implementing termination on a DSLAM, concentration of traffic when implemented cost-effectively produces a performance penalty. The performance penalty occurs by under allocating the access bandwidth of the DSLAM for DLC based terminations. Such under allocation affects all service classes from constant bit rate (CBR) services to unspecified bit rate (UBR) services by asymmetrically concentrating ports of DSL standard communication (xDSL) directly on the DSLAM with xDSL ports that already have been concentrated at the DLC site.
CBR service is impacted by the way a call admission & control (CAC) unit at the DLC handles bandwidth reservation at the DLC versus bandwidth reservation at the DSLAM. In UBR service, ATM cells originating from a DLC based access port have a higher probability of discard or delay than cells originating from a DSLAM access port. Such discard or delay of cells typically occurs because UBR traffic has to pass through both a DLC based scheduler and a DSLAM scheduler, while the DSLAM has only one scheduler to clear.
When implementing termination on a multi-service access platform, typically with other Layer 3 and 4 applications, the available slot bandwidth is limited to a low number of IMA groups so a limited number of DLC sites can be supported thus resulting in a relatively high cost per T1 circuit.
A suggested implementation of HDSL2 and IMA based virtual private networks (VPNs) is described in a presentation of Kevin Woods, Pairgain Technologies, Inc. dated April 2000 at the Internet site http://www.pairgain.com/presentations/pres.home.asp.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.